magrittr - Ceci n'est pas un pipe.

Introduction

The magrittr package offers a set of operators which promote semantics that will improve your code by

structuring sequences of data operations left-to-right (as opposed to from the inside and out),

avoiding nested function calls,

minimizing the need for local variables and function definitions, and

making it easy to add steps anywhere in the sequence of operations.

The operators pipe their left-hand side values forward into expressions that appear on the right-hand side, i.e. one can replace f(x) with x %>% f, where %>% is the (main) pipe-operator. When coupling several function calls with the pipe-operator, the benefit will become more apparent. Consider this pseudo example

Four operations are performed to arrive at the desired data set, and they are written in a natural order: the same as the order of execution. Also, no temporary variables are needed. If yet another operation is required, it is straight-forward to add to the sequence of operations wherever it may be needed.

Installation

To install the current development version use devtools:

devtools::install_github("smbache/magrittr")

To install the CRAN version:

install.packages("magrittr")

Features

Basic piping:

x %>% f is equivalent to f(x)

x %>% f(y) is equivalent to f(x, y)

x %>% f %>% g %>% h is equivalent to h(g(f(x)))

The argument placeholder

x %>% f(y, .) is equivalent to f(y, x)

x %>% f(y, z = .) is equivalent to f(y, z = x)

Re-using the placeholder for attributes

It is straight-forward to use the placeholder several times in a right-hand side expression. However, when the placeholder only appears in a nested expressions magrittr will still apply the first-argument rule. The reason is that in most cases this results more clean code.

Tee operations

Some right-hand sides are used for their side effect (e.g. plotting, printing to a file, etc) and it may be convenient to be able to subsequently continue the pipeline. The "tee" operator, %T>% can be used for this purpose and works exactly like %>%, except it returns the left-hand side value, rather than the potential result of the right-hand side operation:

Pipe with exposition of variables

Many functions accept a data argument, e.g. lm and aggregate, which is very useful in a pipeline where data is first processed and then passed into such a function. There are also functions that do not have a data argument, for which it is useful to expose the variables in the data. This is done with the %$% operator: